The only one of the bunch that I've read is Cry Wolf. I love the main characters a lot, so much so that I prefer the Alpha and Omega books to the author's Mercy Thompson stuff. However, I have to admit that the stories Anna and Charles are in aren't always so great. I can't even remember what they did in this particular book, aside from the cover being a terrible fit for the contents.
Oh wait, I just remembered that I listened to WARP - the image was different, so I didn't connect it. The narrator was good, but the book, not so much unfortunately.
Wow, you aren't kidding about that book cover. I know this will make me sound like a shallow git but I wouldn't pick it up just because of the way it looks.
Warp has some mixed reviews but none of the reviews are from people I know. Most readers seem to hate it or feel meh about it. I might have to scratch that one off the list.
Good luck deciding.
+1 Grave Mercy
+1 Code Name Verity
- 1 WARP
http://lg.booklikes.com/post/900309/w-a-r-p-book-1-the-reluctant-assassin-audio-book-by-eoin-colfer-narrated-by-maxwell-caulfield